Physicists and biologists have published a study detailing how underground analysis of fire ants proves the little critters have a lot to teach future search and rescue robots about working in cramped spaces.

The insects, Solenopsis invicta, thrive underground, where they make nests and forage for food in tunnels and chambers.

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The ants appear to have a knack for never sparking tunnel collapses, one of the major risks related to robots or even humans sabotaging delicate disaster operations. On top of that, they move at great speeds and with ease through the tunnels, scrambling over each other and toppling over without ever seeming to do any real damage to their lair. The Georgia Tech team behind the study realised the insects could be the ideal inspiration for building future underground robots. "The problems that the ants face are the same kinds of problems that a digging robot working in a confined space would potentially face -- the need for rapid movement, stability and safety -- all with limited sensing and brain power," Michael Goodisman, biology professor and coauthor on the paper, said in a statement. "If we want to build machines that dig, we can build in controls like these ants have."

After analysing the subterranean world created by the ants using video tracking and homemade X-ray computed tomography (to enable them to spy on the ants in a more natural habitat, rather than in transparent tubes), the Georgia Tech team found the ants were building tunnels in such a way that a misstep would not cause a total collapse. In addition, they were using their antennae not only for sensing, but for stabilisation. They conclude that key to search missions underground is the ability to mimic the ants in constructing an environment that "simplifies their control task", and thus allows the robots to react to falls "without need for rapid nervous system intervention" -- i.e. not much brain power.

The team allowed the ants to build tunnels in a connected maze of tubes of soil over the course of 20 hours, using soil particles sized from 50 to 600 microns in alternating tubes, with moisture levels of between one and 20 percent. Whatever the variables, the ants continued to build tunnels around about the size of their own bodies, with only the depth and number of tunnels affected by changes to the soil.

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The team realised that the size is directly related to the tunnel safety -- if the tunnel is no bigger than the ants themselves, there's less surface area and therefore fewer opportunities to disturb soil unduly. There's also an additional, more suprising reason. To make sure the insects did in fact trip and fall every now and then, an air piston the tubes were mounted on was fired every so often. At these points, the ants actually used their antennae like little grippers, grabbing on to the walls of the tunnels to stabilise. Having the tunnels no wider than the ants own body length meant they were more likely to be able to grab hold of some soil in time. Goodisman said he was stunned when he saw this novel use of the antenna . "Ants can move rapidly within these environments; their tunnels allow for effective limb, body, and antennae interaction with walls, which facilitate rapid slip-recovery during ascending and descending climbs," write the authors.

Key to trusting a robot in a search and rescue mission is ensuring it does not have to have highly evolved senses in order to survive. The ants use reactionary behaviour to save themselves, build tunnels small enough to always grab on to and double up use of their antenna -- using it as both a sensing device to know when soil's moving, and an extra limb to grab on tight.

It's far from the first time inspiration has been stolen from the natural world to build robots. Roboticists have already used the natural movements of flies, jellyfish and cockroaches, to name just a few, while swarm behaviour has been mimicked in the engineering of next generation drones.